1. Field of the Invention
The present invention concerns a hub for a propeller with variable pitch blades for a turbomachine of the unducted fan or open rotor type.
2. Description of the Related Art
The fan of a turbomachine of this type typically comprises coaxial external upstream and downstream contrarotating propellers each driven in rotation by a turbine of the turbomachine and extending substantially radially outside the nacelle of the turbomachine.
Each propeller comprises a hub including a rotor element of the turbine and a polygonal ring fixed to said rotor element and having substantially radial cylindrical housings distributed around the longitudinal axis of the turbomachine and receiving the blades of the propeller.
The blades may turn in the housings of the polygonal ring and are driven in rotation about the axes of the blades by appropriate means to adjust the angular pitch of the blades to optimize it as a function of the operating conditions of the turbomachine.
In operation, the blades of the propeller are subjected to very high centrifugal forces, as high as 30 000 daN, which forces are transmitted to the polygonal ring. In the event of fracture of the polygonal ring, the blades could escape, causing very extensive structural damage around the turbomachine.